Chemical heat pump working according to the absorption or adsorption principle

ABSTRACT

A chemical heat pump working according to the absorption or adsorption principle comprises an active substance and a volatile liquid, wherein the volatile liquid is adapted to be absorbed or be adsorbed by the active substance at a first temperature and be desorbed by the active substance at a second higher temperature, wherein the chemical heat pump further comprises at least a first tube and at least a second tube, wherein the second tube is at least partially positioned within the first tube and essentially along at least a part of the longitudinal axis of said first tube, wherein the active substance is applied at least partially in a space between the inside of the first tube and the outside of the first tube, wherein a first matrix adapted for storage of the volatile liquid is at least partially applied on the outside of the second tube.

TECHNICAL FIELD

The present invention relates in general to an improved chemical heat pump.

BACKGROUND

In prior art heat pumps are described which comprise a unit tube wherein a part of the tube encloses both a reactor and a condenser/evaporator (FIG. 1). An example of such a heat pump according to the state of the art is described in WO 2009/070090.

A disadvantage of the above described unit tube is that the vapor or gas which is formed when a volatile liquid evaporates has to be transported a long way through the unit tube during charge and discharge. Thereby a pressure drop occurs which impairs the possibility of the chemical heat pump to utilize small temperature differences between a heat source and a heat sink. A long transportation path for the gas implies that when the gas/vapor condenses and returns to the liquid phase, there is a risk that the liquid phase is distributed unevenly in the reactor and condenser/evaporator part respectively of the chemical heat pump. Uneven distribution of liquid may lead to gradual loss of efficiency when the heat pump is charged and discharged repeatedly.

Thus there is a need for an improved heat pump with reduced losses and improved durability of the efficiency during long term use.

SUMMARY

It is an object of the present invention to obviate at least some of the disadvantages in the prior art and provide an improved chemical heat pump

The chemical heat pump can be used as a chemical heat pump working according to the absorption principle and also as a chemical heat pump working according to the adsorption principle. In both versions there is a reactor part and a condenser/evaporator part.

In a first aspect there is provided a chemical heat pump working according to the absorption or adsorption principle comprising an active substance and a volatile liquid, wherein the volatile liquid is adapted to be absorbed or be adsorbed by the active substance at a first temperature and be desorbed by the active substance at a second higher temperature, wherein the chemical heat pump further comprises at least a first tube 1 and at least a second tube 2, wherein the second tube 2 is at least partially positioned within the first tube 1 and essentially along at least a part of the longitudinal axis of said first tube 1, wherein the active substance is applied at least partially in a space between the inside 3 of the first tube 1 and the outside 4 of the first tube 2, wherein a first matrix 5 adapted for storage of the volatile liquid is at least partially applied on the outside 4 of the second tube 2.

Further embodiments are defined in the appended claims, which are specifically incorporated herein by reference.

Advantages of the invention compared to the prior art include but are not limited to; less material is required, the manufacture is simpler, the energy efficiency is improved, the lifetime is extended and a lasting high efficiency is obtained, the number of applications is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows a heat pump according to the state of the art comprising a reactor and a condenser/evaporator in different parts of a tube.

FIG. 2 shows a longitudinal cross section of one embodiment of the present chemical heat pump comprising a first tube 1 with an inside 3, a second matrix 10, a fourth heat conducting layer 9, a first layer 6 which is permeable to the volatile liquid in gas phase, a second tube 2 with an outside 4, a first matrix 5, a second layer 7 which is permeable to the volatile liquid in gas phase, and a third layer 8.

FIG. 3 shows a cross section of the chemical heat pump depicted in FIGS. 2, and

FIG. 4 shows a chemical heat pump as a solar panel adapted to be heated by the sun, comprising a second tube 2 and an energy transfer device 11.

DETAILED DESCRIPTION

Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

It must be noted that, as used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

The term “about” as used in connection with a numerical value throughout the description and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. Said interval is ±10%.

“Ceramic material” is used herein to denote an inorganic non-metallic, material that can be crystalline or amorphous.

There is disclosed a chemical heat pump working according to the absorption or adsorption principle comprising an active substance and a volatile liquid, wherein the volatile liquid is adapted to be absorbed or adsorbed by the active substance at a first temperature and desorbed by the active substance at a second higher temperature, the chemical pump further comprises at least one first tube 1 and at-least one second tube 2, the second tube 2 is at least partially positioned inside said first tube 1 and substantially along at least a part of the longitudinal axis of said first tube 1, wherein the active substance is applied at least partially in a space between the inside 3 of the first tube 1 and the outside 4 of the second tube 2, wherein on the outside 4 of the second tube 2 there is at least partially applied a first matrix 5 adapted for storing the volatile liquid.

In one embodiment, the active substance is at least partially positioned on the inside 3 of the first tube 1 and the active substance is kept fixed to the inside 3 of said first tube 1 with a first layer 6 permeable to the volatile liquid in the gas phase. In one embodiment the first layer 6 comprises a metal mesh. In one embodiment the first layer 6 comprises copper.

In one embodiment, the first matrix 5 is held on the outside of the second tube 2 with a second layer 7 permeable to the volatile liquid in gas phase.

In one embodiment at least one third layer 8 is positioned between the inside 3 of the first tube 1 and the outside 4 of the second tube 2 so that gas can pass from the first tube 1 to the second tube 2. This has the advantage that thermal radiation from the reactor part to the condenser/evaporator part is reduced, so that the gas transport between the reactor part and condenser/evaporator part still is allowed. The function of the third layer 8 is to reflect as much as possible of the thermal radiation that emanates from the reactor part towards the condenser/evaporator part. Thereby radiation losses in the chemical heat pump and the condenser/evaporator part is protected from thermal radiation.

The third layer 8 may for example be designed so that the layer surface is always parallel to the adjacent reactor surface. Thanks to the third layer 8, most of the thermal radiation is reflected, including thermal radiation from the reactor and only a small percentage is absorbed by the reflective material. The proportion of thermal radiation that is still absorbed by the reflective material is then transported with low efficiency through the material with low thermal conductivity and will subsequently radiate out from the material. In one embodiment about 90% of the thermal radiation is reflected directly back towards the heat source. From the surface of the third layer 8 there is emitted further heat radiation back to the heat source because only a small part of the remaining about 10% of the thermal radiation of one embodiment can be lead away through the ceramic part of the third layer 8. The proportion of energy which penetrates the third layer 8 is very small, or in one embodiment about 2% of the total radiated energy supply. The third layer 8 also serves as a splash guard to prevent possible scattering of the active substance from the reactor to the condenser/evaporator. In one embodiment, the third layer 8 is adapted to reflect thermal radiation. In one embodiment the third layer 8 comprises a ceramic material coated with a metal. In one embodiment, the ceramic material is glass. In one embodiment, the metal on the ceramic material is copper. In one embodiment, the metal layer has a thickness of 100 Å or less. In one embodiment, the third layer 8 displays a reflectance of thermal radiation in the range 350-550 K of at least 80%, preferably at least 90%.

In one embodiment at least a fourth heat conductive layer 9 is arranged between the inside 3 of the first tube 1 and the active substance. In one embodiment, the fourth heat conductive layer 8 comprises at least one metal. In one embodiment, the fourth heat conductive layer 8 comprises copper. One advantage of the fourth heat conductive layer 8 is that efficient conduction of heat to the active substance is obtained. If the material of the first tube 1 in itself conducts heat well from the external environment to the active substance the need for such a fourth heat conductive layer 8 is reduced.

In one embodiment, the active substance is matter that can adsorb the volatile liquid.

In one embodiment a second matrix 10 is positioned at least partially on the inside 3 of the first tube 1, wherein the second matrix 10 is adapted to store the active substance.

In one embodiment the active substance is a substance that can absorb the volatile liquid. Examples of such substances include but are not limited to metal salts. Examples of metal salts include but are not limited to magnesium chloride, magnesium bromide, lithium bromide, and lithium chloride. In one embodiment the active substance has at the first temperature a solid state, from which the active substance at absorption of the volatile liquid and its gas phase immediately is transformed at least partially to the liquid state or solution phase and at the second temperature has a liquid state or is in solution phase, from which the active substance by desorbing the volatile liquid, in particular its gas phase, immediately transforms at least partially to the solid state.

In one embodiment an energy transfer device 11 is in thermal contact with the first tube 1 wherein the energy transfer device 11 comprises at least one tube with a first and a second end, the first end is positioned lower than the second end and wherein the energy transfer device 11 comprises a fluid. An energy transfer device 11 or a “heat pipe” means a device in which energy can be moved from point A to point B without the use of pumps with mechanical, often moving parts. In a heat pipe or energy transfer device, energy is transferred so that a liquid is for instance in a tube, wherein one end A of the tube (the evaporator part) by heat turns the liquid into gaseous form and whereby the gas subsequently is transported through the lower gas pressure prevailing in the tube's second end B (the condenser part) so that the gas will be liquefied at B which is both relatively higher positioned and colder than A. Due to the lower temperature at B the gas will return to liquid state, i.e. it will be condensed at B. The liquid formed at condenser part B will due to gravity flow back to A, where the liquid after heating again will be transformed to gas phase. This cycle of evaporation at A and condensation at B implies that an amount of energy is moved from A to B with small losses. In one embodiment, the heat conduction of said energy transfer device is regulated. Thus, the thermal conduction can in one embodiment be switched off or switched on. In one embodiment, the regulation is made with a valve. In alternative embodiments, other modes of regulation are possible.

In one, embodiment the tube 1 is adapted to be heated by an energy source.

In one embodiment the tube 1 is adapted to be heated by solar energy.

In one embodiment the tube 1 is in thermal contact with: the cooling system of a combustion engine.

In one embodiment the tube 1 is in thermal contact with a boiler.

In one embodiment the tube 1 is in thermal contact with a district heating plant.

In one embodiment the tube 1 is in contact with a liquid in a district heating plant.

The present chemical heat pump is designed as a first tube 1 with the reactor part and the condenser/evaporator part in the same tube part. In one embodiment the wall of the first tube 1 comprises different materials that are adapted to the intended use. Examples include but are not limited to glass at a solar panel application and metal when using industrial waste heat and other applications.

The active substance along with the optional metal plate 9 and the first metal net 6 represents the reactor part of the chemical heat pump.

Heat exchange to and from the reactor part can be solved in different ways, examples include but are not limited to positioning a metal tube in connection with the reactor part on the inside 3 of the unit tube 1 or by positioning a metal tube directly on the outer side of the unit tube 1. The latter embodiment requires that the unit tube itself conducts heat to and from the reactor part.

The condenser/evaporator part of the chemical heat pump is found in the central cavity of the unit tube 1. A second tube 2 for heat exchange to and from the condenser/evaporator part is arranged in the first tube 1. In one embodiment, the second tube 2 is arranged in the center of the first tube 1. A first matrix 5 is arranged at least partially around the second tube 2. The first matrix 5 is held against the metal tube 2 by a second layer 7. The first matrix 5 together with the second layer 7 is the condenser/evaporator part of the chemical heat pump, where the first matrix 5 is used for storing the volatile liquid.

Both the first layer 6 and the second layer 7 are permeable to the volatile liquid in the gas phase and thus allow a flow of the volatile liquid in the gas phase.

The first tube 1 is sealed and there is vacuum inside it.

During the charging phase the first tube 1 is heated by a heat source. Examples of heat sources include but are not limited to radiation from the sun, heat from a combustion engine, waste heat from a boiler, and waste heat from industrial processes. The heating of the first tube 1 may be direct or through another device. Examples of other devices include, but are not limited to a metal tube on the outside of the first tube 1. The heat is transferred to the reactor part and the active substance, whereby gas desorbs. The transfer of heat to the active substance can be performed in various alternative ways, examples include but are not limited to a metal plate arranged between the inside 3 of the first tube 1 and the active substance, or directly through the inside 3 of the first tube 1.

The gas formed finds its way inwards from the active substance towards the condenser/evaporator part, which during charging of the chemical heat pump is cooled by using a heat-conveying medium circulating in the second tube 2. The gas condenses into a liquid phase that is sucked up into and stored in the first matrix 5.

During discharge the condenser/evaporator part is heated using a heat-conveying medium circulating in the second tube 2. Volatile liquid in gas phase begins to desorb from the liquid phase which is collected in the first matrix 5. The gas finds its way outwards through the second layer 7 and further on to the reactor part. During discharge the reactor part is kept cooled whereby the gas condenses to a liquid phase which is absorbed or adsorbed by the dry active substance.

In the following the advantages of the invention are described in more detail: The invention provides direct cost benefits because less material is required and because of a simplified production process. Material consumption is reduced because a vacuum housing to the condenser/evaporator is not needed when the reactor and condenser/evaporator are enclosed in a common vacuum housing. Material consumption is reduced further since the condenser is placed in an area that is already insulated because of the vacuum conditions and the optional third layer 8. This eliminates the need for insulating materials and a coating of the insulation material. When the condenser of the present invention is integrated inside the reactor the need for a special gas channel is eliminated. The vacuum housing, gas channel and insulation including coating constitute a major part of the material consumption and the total amount of material used is in one embodiment reduced by about 50% compared to the prior art.

The invention achieves increased energy efficiency due to a reduced transport distance for the gas. The distance of the formed gas to be transported between the reactor part and the condenser/evaporator part has radically been reduced. The gas moves essentially in a radial direction in the device according to the present invention. Thanks to the essential radial transport of the gas, the average transport distance of the gas is only a fraction compared to the prior art.

The shortened transport distance of the gas leads to a significantly lowered pressure drop. The pressure drop can be approximated using the formula below:

${{Pressure}\mspace{14mu} {drop}} = {{32\frac{\mu \; {wL}}{D_{h}^{2}}} + {\sum{\xi_{i}\frac{\rho \; w^{2}}{2}}}}$

wherein

μ=viscosity of the gas

w=velocity of the gas

L=transport distance of the gas

D_(h)=hydraulic diameter

ρ=density

ξ_(i)=coefficient for local resistance.

Compared with the chemical heat pumps according to the art, the shortened gas transport distance of the present invention implies a reduction of the pressure drop which can result in a pressure loss which is only a fraction of the pressure drop according to the prior art. The reduced pressure drop in turn results in a noticeable increase of the usable energy and that cooling can be delivered with the same efficiency at a lower temperature and higher temperature, respectively, with the same efficiency for heating.

The invention provides extended service life with sustained high performance. The risk for an uneven distribution of liquid in the matrix is reduced because the distance over which the gas travels is short and also uniformly distributed over the reactor and the condenser/evaporator, respectively. There are no disadvantaged positions such as in the prior art. This results in a prolonged service life and maintained efficiency during the entire service life.

The invention provides an extended range of applications. The first tube 1 can be produced in virtually any length because the gas transportation is not dependent on the length of the first tube 1, but instead on its diameter. The first tube 1 can for example consist of glass and as a solar collector, but it can also consist of a copper tube. Because the first tube 1 is virtually not dependent on the length, the number of applications is increased because the chemical heat pump can be flexibly adapted to the product of the chemical heat pump to operate in. Examples of such products include but are not limited to:

All sizes of commercially available solar collectors

Heat pumps for cooling or heating with waste heat from a combustion engine.

Heat pumps for cooling or heating with waste heat from a boiler.

Heat pumps for heating or cooling directly from a pipe of a district heating installation.

Energy transport of industrial waste heat.

EXAMPLE

Tests were conducted in a chemical heat pump according to the present invention. Testing was conducted in a test station where the rays of the sun could be simulated under different conditions. As the active substance LiCl was used and the volatile liquid was water. The active substance was stored in a matrix in the reactor part of the chemical heat pump.

The chemical heat pump was charged in the test station using simulated sunlight during about 12 hours. Water evaporated during the charge and was transported from the reactor part to the condenser part of the chemical heat pump. In the cooled condenser part the steam condensed back into water.

Since the gas transport distance of this chemical heat pump has been reduced substantially compared to previously known chemical heat pumps, an increased measured power was expected in the present test. After the chemical heat pump had charged and discharged about 3 times, an average power of 140 W was measured at discharge. By comparison, the average powers during the discharge of known chemical heat pumps, where the same kind of active substance (LiCl) and the same concentration of this substance in the same volatile solvent (water) was used, measured about 40 W. From these tests it can be concluded that this chemical heat pump in this experiment gives an approximately 3.5-fold higher power at discharge than previously known chemical heat pumps.

Other features and uses of the invention and their associated advantages will be evident to a person skilled in the art upon reading the description and the examples.

It is to be understood that this invention is not limited to the particular embodiments shown here. The following examples are provided for illustrative purposes and are not intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof. 

1. A chemical heat pump working according to the absorption or adsorption principle comprising an active substance and a volatile liquid, wherein the volatile liquid is adapted to be absorbed or be adsorbed by the active substance at a first temperature and be desorbed by the active substance at a second higher temperature, wherein the chemical heat pump further comprises at least a first tube and at least a second tube, wherein the second tube is at least partially positioned within the first tube and essentially along at least a part of the longitudinal axis of said first tube, wherein the active substance is applied at least partially in a space between the inside of the first tube and the outside of the second tube, wherein a first matrix adapted for storage of the volatile liquid is at least partially applied on the outside of the second tube.
 2. The chemical head pump according to claim 1, wherein the active substance is at least partially positioned on the inside of the first tube and wherein the active substance is kept fixed to the inside of said first tube with a first layer, permeable to the volatile liquid in gas phase.
 3. The chemical heat pump according to claim 1, wherein said first matrix is fixed to the outside of the second tube with a second layer which is permeable to the volatile liquid in gas phase.
 4. The chemical heat pump according to claim 1, wherein at least one third layer is positioned between the inside of the first tube and the outside of the second tube so that gas can pass from the first tube to the second tube wherein the third layer is adapted to reflect thermal radiation.
 5. The chemical heat pump according to claim 4, wherein the third layer comprises a ceramic material coated with a metal.
 6. The chemical heat pump according to claim 5, wherein the ceramic material is glass.
 7. The chemical heat pump according to claim 5, where the metal is copper.
 8. The chemical heat pump according to claim 5, where the metal forms a layer wherein the thickness of said layer is less than 100 Å.
 9. The chemical heat pump according to claim 6, where the third layer exhibits a reflectance of thermal radiation in the range 350-550 K of at least 80%, preferably at least 90%.
 10. The chemical heat pump according to claim 1, wherein at least a fourth heat conductive layer is arranged between the inside of the first tube and the active substance.
 11. The chemical heat pump according to claim 10, wherein the fourth heat conductive layer comprises at least one metal.
 12. The chemical heat pump according to claim 10, where the fourth heat conductive layer comprises copper.
 13. The chemical heat pump according to claim 1, wherein further a second matrix is positioned at least partially on the inside of the first tube, whereby the second matrix is adapted to store the active substance.
 14. The chemical heat pump according to claim 1, wherein the active substance at the first temperature has a solid state, from which the active substance at uptake of the volatile liquid and its gas phase immediately transforms partially into liquid state or solution phase and at the second temperature has a liquid state or is present in solution phase, from which the active substance by desorbing the volatile liquid, in particular its gas phase, immediately transforms partially to solid state.
 15. The chemical heat pump according to claim 1, wherein an energy transfer device is in thermal contact with the first tube, wherein the energy transfer device comprises at least one tube with a first and a second end, the first end being situated lower than the other end and wherein the energy transfer device comprises a liquid.
 16. The chemical heat pump according to claim 15, wherein the heat conductivity of said energy transfer device can be regulated.
 17. The chemical heat pump according to claim 1, wherein the tube is adapted to be heated by an energy source.
 18. The chemical heat pump according to claim 1, wherein the tube is adapted to be heated by solar energy.
 19. The chemical heat pump according to claim 1, wherein the tube is in thermal contact with the cooling system of a combustion engine.
 20. The chemical heat pump according to claim 1, wherein the tube is in thermal contact with a boiler.
 21. The chemical heat pump according to claim 1, wherein the tube is in thermal contact with a district heating plant.
 22. The chemical heat pump according to claim 21, wherein the tube is in contact with a liquid in a district heating plant. 